Comparison of MLC positioning deviations using log files and establishment of specific assessment parameters for different accelerators with IMRT and VMAT

Abstract

Background and purpose The study evaluated the differences in leaf positioning deviations by the log files of three advanced accelerators with two delivery techniques, and established specific assessment parameters of leaf positioning deviations for different types of accelerators. Methods A total of 420 treatment plans with 5 consecutive treatment log files were collected from the Trilogy, TrueBeam and Halcyon accelerators. Millennium MLC was equipped on the Trilogy and TrueBeam accelerators. A jawless design and dual-layer MLC were adopted on the Halcyon accelerator. 70 IMRT and 70 VMAT plans were selected randomly on each accelerator. The treatment sites of all plans included head and neck, chest, breast, pelvis and other sites. The parsing tasks for 2100 log files were proceeded by SunCheck software from Sun Nuclear Corporation. The maximum leaf root mean square (RMS) errors, 95th percentile errors and percentages of different leaf positioning errors were statistically analyzed. The correlations between these evaluation parameters and accelerator performance parameters (maximum leaf speed, mean leaf speed, gantry and arc angle) were analyzed. Results The average maximum leaf RMS errors of the Trilogy in the IMRT and VMAT plans were 0.44 ± 0.09 mm and 0.79 ± 0.07 mm, respectively, which were higher than the TrueBeam's 0.03 ± 0.01 mm, 0.03 ± 0.01 mm and the Halcyon's 0.05 ± 0.01 mm, 0.07 ± 0.01 mm. Similar data results were shown in the 95th percentile error. The maximum leaf RMS errors were strongly correlated with the 95th percentile errors (Pearson index > 0.5). The leaf positioning deviations in VMAT were higher than those in IMRT for all accelerators. In TrueBeam and Halcyon, leaf position errors above 1 mm were not found in IMRT and VMAT plans. The main influencing factor of leaf positioning deviation was the leaf speed, which has no strong correlation with gantry and arc angles. Conclusions Compared with the quality assurance guidelines, the MLC positioning deviations tolerances of the three accelerators should be tightened. For both IMRT and VMAT techniques, the 95th percentile error and the maximum RMS error are suggested to be tightened to 1.5 and 1 mm respectively for the Trilogy accelerator. In TrueBeam and Halcyon accelerators, the 95th percentile error and maximum RMS error of 1 and 0.5 mm, respectively, are considered appropriate.

Characterization of a novel VenusX orthogonal dual‐layer multileaf collimator

“…The multileaf collimator (MLC) is the most widely used tool for modulating beam fluence in intensity‐modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) 1–5 . MLC has been used in radiotherapy for over 30 years, 6,7 and its design characteristics influence treatment plan dose distributions 8–14 .…”

Three-dimensional semiconductor detector array ArcCHECK for radiation detection and quality assurance of medical linear acceleration

“…Continuous single (or multiple) arc therapy in VMAT can be achieved with gantry rotation speed, multi-leaf collimator (MLC) leaf movement, and dose rate variation during radiation delivery, which is more complex than IMRT. For VMAT treatment plans, the accuracy of the MLC position, position deviation caused by gravity during gantry rotation, and beam atness and symmetry have a signi cant impact on the implementation of radiotherapy 4,5 . Hence, there is a need to conduct daily radiation detection and quality assurance research on the VMAT technique to ensure the safe and accurate implementation of radiotherapy.…”

Dosimetric impact of MLC positional errors on dose distribution in IMRT

“…Dose variation and positional accuracy due to MLC positional error for modern irradiation methods such as multiple brain metastases using linear accelerators have been studied 12 . Other reports have also been published comparing the detection ability of MLC positional errors to tools such as the log file and EPID (Electronic Portal Imaging Devices) for detecting MLC misalignment 13–15 . Furthermore, an algorithm has been developed recently to predict MLC position discrepancies using machine learning and its prediction accuracy has been studied 16–20 .…”

“…Furthermore, an algorithm has been developed recently to predict MLC position discrepancies using machine learning and its prediction accuracy has been studied 16–20 . Among the mechanical parameters, dose errors due to MLC positional errors have the largest impact, and many studies have been conducted to examine its impact and prediction accuracy 1–20 …”

“…[16][17][18][19][20] Among the mechanical parameters, dose errors due to MLC positional errors have the largest impact, and many studies have been conducted to examine its impact and prediction accuracy. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] This study focused on the identification of the clinical situations that affect the MLC sequence and change the dose error among the various combinations of radiotherapy techniques. Recent developments in equipment and radiation oncology have increased the number of treatment sites to which VMAT and hypofractionated radiotherapy are applied.…”